1. Field of the Invention
This invention relates to a new storage-stable melamine composition for improving the effectiveness of melamine use, and to a method for preparing the composition. More particularly, this invention relates to a composition of a storage-stable dispersion of melamine which provides concentrated melamine for direct use, or for conversion into other valuable products. Dust and handling losses normally incurred in handling dry melamine powder are virtually eliminated.
2. Description of Related Art
Melamine, 2,4,6-triamino-1,3,5-triazine, a white crystalline powder, with a water solubility at room temperature of 0.5% (5000 ppm) and nitrogen content of 66.67%, is a versatile chemical compound used primarily to react chemically with other compounds to prepare resins and plastics. Recently several important new uses for melamine, in the unreacted form, have been disclosed. Melamine has been reported to provide fire retardancy when incorporated into a variety of otherwise flammable materials, including plastic sheets and foams. Melamine also has been found to be valuable in agriculture as a plant food, a nitrification inhibitor, and a non-protein nitrogen ruminant feed supplement.
Melamine is conventionally shipped in bulk by tank truck and rail hopper car, or contained in large plastic bags containing about 1000 pounds, and, usually, in paper bags containing about 50 pounds. Melamine when received for further processing is usually a dusty powder containing some soft aggregates. Direct utilization of this commercial melamine product as an ingredient in resins, plastics, or agricultural formulations creates problems in storing, conveying, and dispensing because melamine dust is lost, and it has a tendency to aggregate to form a powder bridge across openings, clogging chutes, conveyors or other transfer or storage equipment. The dust lost in the handling process is irritating to workers, economically costly, and requires installation of dust-venting systems.
Various techniques have been disclosed in the art to ease the problems of handling melamine. All of the techniques disclosed require undesirable additional chemical reactions or substantial dilutions. In U.S. Pat. No. 2,603,614, Nieson and Nason prepared a glow proofing compound from a phenolic resin, and the chemical reaction product of melamine, formaldehyde, and phosphorus pentoxide. The final reaction product was a dry powder which could be handled by suspending in water with the aid of dispersing agents. The suspension was applied to fibrous materials which were then formed into insulating blocks. Considerable effort and cost were required to put the melamine powder in a useful form.
Wohnsiedler and Thomas in U.S. Pat. No. 2,485,079 disclosed a colloidal melamine-urea-formaldehyde copolymer solution to impart good flame-proofing to cotton fibers. The solution was prepared from urea and melamine chemically reacted with formaldehyde by means of an acid catalyst. The processing and dilution of melamine required to make the copolymer useful was extensive.
Handling melamine in the preparation of plastics was improved by Tzeng and Moore in U.S. Pat. No. 2,797,206, disclosing a stable melamine-urea-formaldehyde sirup formed by the base catalyzed reaction of urea-formaldehyde and melamine in aqueous methanol solution. Melamine was put in stable form but chemical reaction was required.
In a similar manner, David Chalmers disclosed, in British Patent No. 889,260, another stable melamine-formaldehyde resin sirup also using formaldehyde in aqueous methanol as a reactant, but with dicyandiamide added as a stabilizer. Methanol is undersirable in many melamine uses and dicyandiamide is costly material which also is not desirable in some melamine uses.
Izumi, Kitto, and Ito in Japanese Kokai 73/31,291 disclose an example of the very complicated procedures developed for the effective use of melamine. This publication teaches improvements in the solubility and storage stability of melamine by preparation of a melamine formaldehyde preconcentrate containing large amounts of stabilizing tetramethylolmelamine, by dissolving a formaldehyde-melamine preconcentrate in a pyridine-chloroform mixture and then fractionating the solution into desirable materials by treatment in a cellulose-filled absorption column.
Melamine has been found to be an effective fire retardant for plastic forms, including foams. To prepare these materials, melamine has been used as a solid or in the liquid resin form, usually as a melamine-formaldehyde concentrate, pre-resin, or resin. The formaldehyde has been used because it offers a convenient way of handling the melamine as a liquid, and facilitates its introduction into the final fire-retardant product. Unfortunately, formaldehyde dilutes the melamine and reduces flame retardancy of the final product. The use of melamine as a solid presents the problems normally associated with the use of fine particle powders.
Oesterreichische Stickstoffwerke A.G. disclosed in French Patent No. 2,102,029 preparation of fire-resistant moldings from substantial amounts of melamine mixed with polyurethane or epoxy resins in a mold at room temperature. The components are held overnight in a mold to harden, and then unmolded to produce epoxy or urethane plastics with low combustibility ratings. Preparation of a flame-retarding fine cell polyurethane foam by a similar method was also disclosed. Unfortunately, no convenient method for introducing the melamine into the reaction mixture was suggested.
Melamine has been used in agriculture as a fertilizer, a foliar feed, and as a ruminant feed supplement. Ludecke and Nitzsche in Ger. Landwirtch. Forsch. 11, 167-78 (1958), reported that spraying dilute melamine solution on sugar beet foliage significantly increased yield at suitable melamine solution concentrations in water.
Another agricultural use reported for melamine is that of a protein substitute in ruminant feed supplements. B. B. Wilson discloses in U.S. Pat. No. 3,653,909 that melamine included in ruminant feed supplements improves the nitrogen intake of the animals consuming it, and increases the desirable production of volatile fatty acids in the rumen of the animals. The liquid supplement contained urea, salt, melamine, minerals, vitamins, ammonium polyphosphate solution, water, and molasses. The melamine used in the liquid supplements was limited to minor concentrations, and was blended with many other materials.
The melamine compositions and methods described briefly in the foregoing paragraphs utilized various modifications of melamine to make the melamine suitable for handling, storing, or conversion to other end use products. Most of these compositions involved significant dilutions of melamine, the chemical reaction of melamine with other ingredients to form storage-stable liquids, or the inclusion of melamine with substantial amounts of additives which could affect the properties of melamine. In many uses it is undesirable to have melamine diluted, chemically reacted, or mixed with substantial amounts of other materials. The use of melamine as the undiluted compound is particularly important where the melamine is to be used as a fire-retarding agent, or as an agricultural product. None of the prior art disclosed a concentrated storage-stable liquid dispersion of melamine containing inconsequentially low concentrations of suspending agents; and no method is suggested for preparing such a dispersion.